How do you specify what file you want to send? Under 'Send to device', 'Send specific format', the only choice available is 'Main Memory' (the grayed out choices are 'Memory Card A' and 'Memory Card B'. There's nothing about any formats like mobi, pdf, or text, etc.

If you actually select the 'Send to device' - 'Send specific format' - 'Main Memory' option the next thing that happens is a list of formats comes up and you can select MOBI from it.